The Magic Key — Emily Rodda

Enter the realm of enchantment.

Jessie returns to the magical Realm for the fifth time. The magic of the Realm has rescued her home from terrible fires, and she has saved the Realm's magical people from a wicked imposter, kept the griffin guards under control, and saved the fairy-apple trees.

Now it's Jessie's birthday, and she finds herself chasing a rainbow. She's got to get to the end before it fades, or she may never get home!

Then there are the Rainbow Fairies, who desperately need Jessie's help to find a lost magic treasure. Until it's found, they'll never get back to the secret garden.